RLP retransmission for CDMA communication systems

ABSTRACT

Techniques for retransmitting data via RLP in a CDMA (e.g., cdma2000) system with a first retransmission mechanism provided by the RLP and a second retransmission mechanism provided by an HARQ-CF. In one method, missing RLP frames are first detected (e.g., by a receiver RLP). A dynamic timer is then maintained (e.g., by a receiver HARQ-CF) for each RLP frame detected to be missing. The dynamic timers are event-driven and have variable time durations. Each dynamic timer is updated based on events known to the receiver HARQ-CF. Fixed timers with fixed time durations may also be maintained (e.g., by the receiver RLP) for the missing RLP frames. Whether or not a missing RLP frame is lost is determined based on the dynamic timer and the fixed timer (if any) maintained for the RLP frame. A NAK may be issued for retransmission of each RLP frame deemed to be lost.

BACKGROUND

[0001] 1. Field

[0002] The present invention relates generally to data communication,and more specifically to techniques for retransmitting packets by aRadio Link Protocol (RLP) in CDMA communication systems.

[0003] 2. Background

[0004] Wireless communication systems are widely deployed to providevarious types of services such as voice, packet data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users, and may be based on code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), or some other multiple accesstechniques. CDMA systems may provide certain advantages over other typesof system, including increased system capacity.

[0005] To improve the reliability of data transmission, many CDMAsystems employ a retransmission mechanism provided by a Radio LinkProtocol (RLP) that resides above the physical layer. An RLP entity atthe receiver (i.e., the receiver RLP) is provided with RLP frames by alower-level entity, with each RLP frame being uniquely identified by itsassigned sequence number. Since the RLP frames to be transmitted areassigned sequential sequence numbers, the receiver RLP is able todetermine whether or not any RLP frames are missing by looking at thesequence numbers of the received RLP frames. In the absence of any otherretransmission mechanism, the RLP frames may be transmitted serially tothe receiver, and any RLP frame detected to be missing by the receiverRLP may be immediately reported to the transmitter via a transmission ofa negative acknowledgment (NAK). The missing RLP frames may thereafterbe retransmitted to the receiver.

[0006] To provide improved packet data transmission capability, somenewer-generation CDMA systems (e.g., cdma2000 Release C) employ anotherretransmission mechanism provided by a hybrid automatic retransmissioncontrol function (HARQ-CF) that resides between the RLP and the physicallayer. The HARQ-CF defined by cdma2000 is able to transmit multiple HARQpackets in parallel, with each HARQ packet including one or more RLPframes. Moreover, because each HARQ packet may betransmitted/retransmitted once or multiple times by the HARQ-CF, theHARQ packets may be recovered in an unknown order by the HARQ-CF entityat the receiver (i.e., the receiver HARQ-CF). Thus, RLP frames may beprovided out of sequence to the receiver RLP. In addition, because ofretransmission by the HARQ-CF, the receiver RLP may have to wait a longtime period before it can determine with confidence that a given missingRLP is really lost. The HARQ-CF retransmission may thus severely impactthe performance of the RLP retransmission.

[0007] There is therefore a need in the art for an RLP retransmissionscheme that can operate efficiently in conjunction with the underlyingHARQ-CF retransmission mechanism.

SUMMARY

[0008] Techniques are provided herein to exploit the functionality ofthe RLP and HARQ-CF so that they can operate in a seamless and efficientmanner to improve system performance. These techniques utilize differentinformation available at different entities to implement an RLPtransmission scheme that can provide improved performance.

[0009] In an embodiment, a method is provided for retransmitting datavia the RLP in a CDMA (e.g., cdma2000) communication system with a firstretransmission mechanism provided by the RLP and a second retransmissionmechanism provided by the HARQ-CF. In accordance with the method,missing RLP frames are first detected (e.g., by the receiver RLP). Adynamic timer is then maintained (e.g., by the receiver HARQ-CF) foreach RLP frame detected to be missing. Each dynamic timer is thereafterupdated based on events known to the receiver HARQ-CF, and theexpiration of each dynamic timer is triggered by these events. Fixedtimers with fixed time durations may also be maintained (e.g., by thereceiver RLP) for the missing RLP frames. The determination of whetheror not each missing RLP frame is lost is then made based on the dynamictimer (and the fixed timer, if any) maintained for the RLP frame. A NAKmay then be issued (e.g., by the receiver RLP) for retransmission ofeach RLP frame deemed to be lost.

[0010] In an embodiment, the dynamic timers are event-driven, and eachdynamic timer has a variable time duration that is determined by eventsknown to the receiver HARQ-CF. For cdma2000, the RLP frames are includedin HARQ packets transmitted by the HARQ-CF, and each HARQ packet may betransmitted on any one of a number of possible ARQ channels (which maybe viewed as logical channels). The dynamic timer for each missing RLPframe may then be associated with a respective candidate set of ARQchannels that may be used to transmit the HARQ packet that includes themissing RLP frame. Each ARQ channel in a candidate set may be removedfrom the set if it is determined that the ARQ channel could not be theone used to transmit the missing RLP frame. The dynamic timer for eachRLP frame then expires when the associated candidate set becomes empty,since this means that there is no ARQ channel left that could be used totransmit the missing RLP frame.

[0011] The characteristics of the HARQ-CF may be used to select a set ofcriteria used to remove ARQ channels from candidate sets. For cdma2000,an ARQ channel may be removed from a candidate set if any one of thefollowing events occurs after the dynamic timer is triggered: (1) a goodHARQ packet is received via the ARQ channel, (2) a new HARQ packet istransmitted via the ARQ channel, or (3) no transmission is received viathe ARQ channel within a particular period. These criteria are describedin further detail below.

[0012] In general, the techniques described herein may be used forretransmitting data in any wireless communication system with a firstretransmission mechanism in a first sublayer (e.g., RLP) and a secondretransmission mechanism in a second sublayer (e.g., HARQ-CF), where thesecond sublayer resides below the first sublayer in the protocol stack.

[0013] Various aspects and embodiments of the invention are described infurther detail below. The invention further provides methods, programcodes, digital signal processors, receiver units, transmitter units,terminals, base stations, systems, and other apparatuses and elementsthat implement various aspects, embodiments, and features of theinvention, as described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The features, nature, and advantages of the present inventionwill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

[0015]FIG. 1 is a diagram of a CDMA communication system;

[0016]FIG. 2 is a diagram of a layer structure defined by cdma2000Release C;

[0017]FIG. 3 is a diagram illustrating the data encapsulation performedby a base station for data transmission on a packet data channel;

[0018]FIG. 4 is a timing diagram illustrating an example datatransmission on the packet data channel;

[0019]FIG. 5 is a diagram illustrating the interaction between areceiver RLP and a receiver HARQ-CF for data transmission on the packetdata channel;

[0020]FIG. 6 is a diagram illustrating the interaction between thereceiver RLP and receiver HARQ-CF for data transmission on the packetdata channel with fixed and dynamic timers;

[0021]FIG. 7 is a flow diagram of a process for initiatingretransmission of missing RLP frames at the RLP sublayer based ondynamic timers and fixed timers;

[0022]FIG. 8 is a flow diagram of a process for determining whether ornot a particular missing RLP frame is lost based on transmissions on theF-PDCH; and

[0023]FIG. 9 is a block diagram of an embodiment of a base station and aterminal.

DETAILED DESCRIPTION

[0024]FIG. 1 is a diagram of a CDMA communication system 100 that mayimplement various aspects and embodiments of the RLP retransmissiontechniques described herein. System 100 includes a number of basestations 104 that communicate with a number of terminals 106 (only onebase station and two terminals are shown in FIG. 1 for simplicity). Abase station is a fixed station used for communicating with theterminals. Depending on the context in which the term is used, a basestation may refer to a cell, a sector within a cell, a base transceiversystem (BTS), a mobile station controller (MSC), or other part of thecommunication system. A base station is also referred to as an accesspoint, a Node B, or some other terminology. The base stations may bepart of a UMTS Radio Access Network (UTRAN).

[0025] A terminal is a station that communicates with the base station.A terminal is also referred to as a mobile station, a remote station, anaccess terminal, a user equipment (UE), or some other terminology. Eachterminal may communicate with one or more base stations on the forwardlink and/or reverse link at any given moment, depending on whether ornot the terminal is active, whether or not soft handoff is supported forthe data transmission, and whether or not the terminal is in softhandoff. The forward link (i.e., downlink) refers to transmission fromthe base station to the terminal, and the reverse link (i.e., uplink)refers to transmission from the terminal to the base station.

[0026] The techniques described herein for RLP retransmission may beimplemented in various CDMA communication systems. Thus, CDMA system 100may implement one or more commonly known CDMA standards such ascdma2000, IS-856, W-CDMA, IS-95, and others. For clarity, variousaspects, embodiments, and implementation details for RLP retransmissionare described below for a CDMA system that supports cdma2000 Release C.

[0027] cdma2000 supports various types of services such as voice, packetdata, and so on. cdma2000 Release C further supports high-speed packetdata transmission on the forward link via a packet data channel and anentity that controls the operation of the packet data channel. Thepacket data channel comprises a set of physical channels, which are:

[0028] F-PDCH—forward packet data channel. This physical channel carriesdata for the high-speed packet data transmission.

[0029] F-PDCCH—forward packet data control channel. This physicalchannel carries control information for the F-PDCH.

[0030] R-ACKCH—reverse acknowledgment channel. This physical channelcarries acknowledgment feedback for an automatic retransmission (ARQ)protocol.

[0031] R-CQICH—reverse channel quality indication channel. This physicalchannel carries forward link RF channel quality feedback and is furtherused to indicate a specific base station selected by the terminal forF-PDCH operation.

[0032] The control entity for the packet data channel is referred to asthe packet data channel control function (PDCHCF) entity or the hybridautomatic retransmission control function (HARQ-CF) entity. This controlentity implements procedures for operating the physical channelsassociated with the packet data channel.

[0033]FIG. 2 is a diagram of a layer structure 200 defined by cdma2000Release C. Layer structure 200 includes (1) applications and upper layerprotocols that approximately correspond to Layers 3 through 7 of theISO/OSI reference model, (2) protocols and services that correspond toLayer 2 (the link layer), and (3) protocols and services that correspondto Layer 1 (the physical layer).

[0034] The applications and upper layer protocols utilize the servicesprovided by the sublayers in Layer 2 (i.e., the LAC and MAC sublayers).Examples of supported applications include signaling services 212,packet data services 214, voice services 216, and circuit dataapplications. Layer structure 200 supports a combination of voice,packet data, and circuit data services to operate concurrently.

[0035] Layer 2 includes a Link Access Control (LAC) sublayer 220, aMedium Access Control (MAC) sublayer 230, and a hybrid ARQ controlfunction (HARQ-CF) 240. The MAC sublayer comprises a Radio Link Protocol(RLP) 232 and a multiplexing and QoS sublayer 236 (which is alsoreferred to as the multiplex sublayer). The RLP provides best effortdelivery of packet data to ensure reasonably reliable data transmissionover the radio link. The multiplex sublayer provides the interfacebetween the RLP and HARQ-CF. The multiplex sublayer further implements acontrol mechanism to balance varying quality of service (QoS)requirements of multiple concurrent services to ensure that thenegotiated QoS levels for these services are met. This is achieved bymediating conflicting requests from competing services and prioritizingaccess requests. The structure of the MAC sublayer and the entities thatcomprise the MAC sublayer are described in detail in documentTLA/EIA/IS-2000.3-C, entitled “Medium Access Control (MAC) Standard forcdma2000 Spread Spectrum Systems,” Release C, which is incorporatedherein by reference.

[0036] The HARQ-CF performs a number of functions related to datatransmission on the packet data channel. First the HARQ-CF terminatesall of the physical channels associated with the packet data channel(i.e., the F-PDCH, F-PDCCHs, R-ACKCH, and R-CQICH). Second, the HARQ-CFprovides an automatic retransmission (ARQ) protocol that ensuresreliable delivery of encoder packets from the base station to theterminal via retransmission of portions of encoder packets based onfeedback from the mobile station. This feedback is in the form of anacknowledgment (ACK) to indicate successful decoding of an encoderpacket or a negative acknowledgment (NAK) to indicate an unsuccessfuldecoding of the encoder packet.

[0037] The physical layer provides the mechanism for transmitting datafor the MAC sublayer and signaling for the upper layer. The physicallayer is described in detail in document TIA/EIA/IS-2000.2-C, entitled“Physical Layer Standard for cdma2000 Spread Spectrum Systems,” ReleaseC, which is incorporated herein by reference.

[0038]FIG. 3 is a diagram illustrating the data encapsulation performedby the base station for data transmission on the packet data channel. Incdma2000 Release C, data to be transmitted on the packet data channel toa particular terminal is requested from the data services by themultiplex sublayer. The entity that provides data from a data service tothe multiplex sublayer is the RLP.

[0039] The RLP receives data from the data services and forms RLPframes. Each RLP frame includes a sequence number that uniquelyidentifies the RLP frame and the data from the data service. The RLPthen provides RLP frames to the multiplex sublayer.

[0040] The multiplex sublayer receives the RLP frames, which are simplyviewed as data blocks by this sublayer. The multiplex sublayer thenprocesses each data block by adding a header (H). The combination of theheader and the data block is referred to as a multiplex sublayerProtocol Data Unit (MuxPDU) in cdma2000. The multiplex sublayer thenencapsulates one or more MuxPDUs to form a PDCHCF SDU (Service DataUnit).

[0041] The multiplex sublayer generates a PDCHCF SDU for transmission onthe F-PDCH whenever it receives an indication to do so. To form eachPDCHCF SDU, the multiplex sublayer requests data blocks from logicalchannels that have been mapped to the F-PDCH, in a particular orderbased on the relative priority of each logical channel. This continuesuntil enough data blocks have been supplied to form the number ofMuxPDUs needed to fill the PDCHCF SDU, or until all mapped logicalchannels have supplied all available data blocks. The multiplex sublayerthen creates a MuxPDU for each received data block.

[0042] The multiplex sublayer then serially concatenates one or moreMuxPDUs to form the PDCHCF SDU. The PDCHCF SDU has variable length andmay include any number of MuxPDUs. The specific number of MuxPDUs toinclude in each PDCHCF SDU is determined by the HARQ-CF (i.e., PDCHCF).If the PDCHCF SDU is not completely filled, then the multiplex sublayerinserts one or more padding MuxPDUs to completely fill the PDCHCF SDU.Each padding MuxPDU contains ‘0’ bits. The multiplex sublayer thenprovides the assembled PDCHCF SDU to the HARQ-CF.

[0043] The HARQ-CF processes each PDCHCF SDU received from the multiplexsublayer by appending a 2-bit field (P) at the end of the PDCHCF SDU toform a corresponding PDCH Physical Layer SDU, which is referred toherein as an HARQ packet. The HARQ-CF then provides the HARQ packet tothe physical layer.

[0044] The physical layer Turbo encodes each HARQ packet to generate acorresponding encoder packet. A portion of or the whole encoder packetmay be transmitted via the physical layer channel as a subpacket of theencoder packet. A subpacket is identified by a unique subpacketidentifier (SPID). In particular, an encoder packet can be transmittedas subpackets with SPIDs of ‘0’, ‘1’, ‘2’, and ‘3’. Each subpacketincludes a sufficient amount of coded data to allow the receiver todecode the received subpacket and recover the HARQ packet. Differentsubpackets typically include different portions of an encoder packet.The four subpackets may be viewed as different versions of the encoderpacket.

[0045] Subpackets are typically generated on fly (i.e., dynamically)based the transmit format provided by the HARQ-CF. Specifically, thesubpackets for an encoder packet will correspond to different portionsof the encoder packet if the HARQ-CF determines to use differenttransmit formats, even though the subpackets have the same ACID.

[0046] The physical layer then transmits one subpacket at a time to theterminal in accordance with a defined transmission procedure, asdescribed below.

[0047] When a base station transmits a subpacket of an encoder packet toa particular mobile station, the base station needs to wait for acertain amount of time before receiving any feedback from this terminalfor the transmitted subpacket. This is because it takes time to transmitthe subpacket on the forward link and to transmit the feedback on thereverse link. The associated processing at the base station and at theterminal also takes time. To eliminate dead time and enhanceperformance, the base station may transmit other encoder packets to thesame or another terminal while waiting for the feedback of the encoderpacket from this terminal. This can be done by the HARQ-CF that is usedto support packet data channel transmission on four independent ARQchannels, which may be viewed as four logical channels of the FPDCH.These four ARQ channels permit the base station to transmit up to fourencoder packets in parallel to a given terminal via four pending encoderpacket transactions. Thus, at any given moment, there can be up to fouroutstanding encoder packets (i.e., packets that have not yet beenacknowledged as being correctly received by the terminal).

[0048] The specific number of ARQ channels to use is determined by thebase station and signaled to the terminal. These ARQ channels areuniquely identified by an ARQ channel identifier (ACID) assigned to eachARQ channel. For example, the four ARQ channels may be assigned ACIDs of‘0’, ‘1’, ‘2’, and ‘3’. The ACID for each subpacket transmitted on theF-PDCH is uniquely identified by control information sent on theaccompanying F-PDCCH. Therefore, there is no ambiguity at the terminalregarding what subpackets to combine prior to the decoding operation.

[0049] The HARQ-CF at the base station transmits the subpackets for eachencoder packet in accordance with a set of rules. Each encoder packet istransmitted and possibly retransmitted on a single ARQ channel. For agiven encoder packet, the base station transmits subpacket ‘0’ beforeany other subpackets for the encoder packet. The base station cantransmit subpackets ‘0’, ‘1’, ‘2’, or ‘3’ any number of time, in anyorder and at any time, as long as the total number of subpacketstransmitted for the encoder packet does not exceed eight. The basestation can transmit any subpacket multiple times, and can also omit anysubpacket other than subpacket ‘0’.

[0050] The subpackets for a given encoder packet may be transmitted overdifferent transmission lengths (or durations). It is also possible forthe base station to retransmit the same subpacket more than one timeusing different transmission lengths.

[0051] Because of the redundant information in the subpackets, it ispossible for the terminal to successfully decode the encoder packetbefore all four subpackets have been transmitted. When the terminalreceives a subpacket, it attempts to decode the encoder packet based onall subpackets that have been received for this encoder packet (i.e.,the subpackets for the current and prior transmissions). If the decodingoperation is successful (i.e., the CRC for the encoder packet is valid),then the terminal sends an ACK on the R-ACKCH channel, and the basestation can stop sending subpackets for this encoder packet. Conversely,if the decoding operation is unsuccessful (i.e., the CRC for the encoderpacket is invalid), then the terminal sends a NAK on the R-ACKCHchannel. The base station can use the ACK/NAK feedback from the terminalto transmit additional subpackets for the encoder packet.

[0052] Because the terminal combines current and prior receivedsubpackets for the same encoder packet prior to decoding, a mechanism isprovided to allow the terminal to determine when a subpacket receivedwithin the same ARQ channel (i.e., the same ACID) is for a new encoderpacket. In this way, the terminal can purge subpackets previouslyreceived on the same ARQ channel for a prior encoder packet and startaccumulating subpackets for the new encoder packet. For cdma2000, thismechanism comprises an ARQ identifier sequence (ARQ_IS) number that isincluded in the accompanying control message transmitted the F-PDCCH bythe base station. The ARQ_IS number is a single bit value that togglesbetween ‘0’ and ‘1’ for consecutive encoder packets transmitted on thesame ARQ channel and is effectively a 1-bit sequence number. The ARQ_ISnumber is also referred to herein as the “color” bit.

[0053] When the first subpacket for a new encoder packet is transmittedon an ARQ channel, the receiver is signaled that this is a new encoderpacket by a flipped color bit. In particular, the color bit for allsubpackets of a particular encoder packet transmitted on a given ARQchannel is set to a particular value (e.g., ‘1’), the color bit for allsubpackets of the next encoder packet transmitted on the same ARQchannel is set to the alternate value (e.g., ‘0’), and so on. If thecolor bit for a received subpacket changes (i.e., flips), then theterminal treats this subpacket as the first subpacket for a new encoderpacket and would discard all subpackets previously received on the sameARQ channel.

[0054] Transmissions on all physical channels associated with the packetdata channel occur in unit of slots, where one slot is 1.25 msec forcdma2000. Transmissions on the F-PDCH and F-PDCCH occur over durationsof 1, 2, or 4 slots (i.e., 1.25 msec, 2.5 msec, or 5 msec), andtransmissions on the R-ACKCH occur on 1.25 msec, 2.5 msec, or 5 msecslot intervals.

[0055] When a subpacket is transmitted on an ARQ channel, the packetdata portion is transmitted on the F-PDCH and the corresponding controlinformation is transmitted as a message on one of two F-PDCCHs, F-PDCCH0and F-PDCCH1. When a terminal is assigned to the packet data channel, itis assigned a MAC identifier (MAC_ID) to uniquely address the terminalon the two shared F-PDCCHs. Messages on the F-PDCCHs are targeted tospecific terminals by setting a MAC_ID field in each F-PDCCH SDU to theMAC_ID assigned to the terminal designated to receive the subpacketbeing transmitted on the F-PDCH.

[0056] Messages may be sent to the terminal on either of the twoF-PDCCHs starting at any slot when the terminal is assigned to thepacket data channel. Thus, the terminal would need to continuouslymonitor and process F-PDCCH0 to receive control messages. If no messagewere received on F-PDCCH0 dedicated for the terminal, then the terminalwould also need to process F-PDCCH1 for the same time interval. If acontrol message received on either F-PDCCH0 or F-PDCCH1 indicates that asubpacket is transmitted to the terminal on the F-PDCH, then theterminal processes the F-PDCH to recover the subpacket. For simplicity,both F-PDCCH0 and also F-PDCCH1 are collectively referred to herein asthe F-PDCCH.

[0057]FIG. 4 is a timing diagram illustrating an example datatransmission on the packet data channel. This example shows threesubpackets being transmitted with an ACK_DELAY of two slots. ACK_DELAYspecifies the number of slots between the end of an F-PDCH transmissionand the beginning of an R-ACKCH transmission for the correspondingF-PDCH transmission.

[0058] At time T₁, a two-slot message is transmitted on the F-PDCCH forthe first subpacket assignment. This message indicates the initialtransmission for a first ARQ channel, with SPID=‘0’ and ACID=‘0’. Sincethe duration of the F-PDCCH message is two slots, the transmission ofsubpacket ‘0’ on the F-PDCH is also two slots. In this example, theterminal receives the control message on the F-PDCCH, processes theF-PDCH, but fails to recover the HARQ packet for the first ARQ channelbased on the received subpacket ‘0’. The terminal subsequently sends aNAK on the R-ACKCH at time T₃, which is two slots (or ACK_DELAY slots)after the end of the F-PDCH transmission at time T₂.

[0059] At time T₃, a four-slot message is transmitted on the F-PDCCH fora new subpacket assignment. This message indicates the initialtransmission for a second ARQ channel, with SPID=‘0’ and ACID=‘1’. Sincethe duration of the F-PDCCH message is four slots, the duration of thesubpacket transmission on the F-PDCH is also four slots. In thisexample, the terminal is able to correctly decode the encoder packet forthe second ARQ channel based on the received subpacket ‘0’. The terminalthen sends an ACK on the R-ACKCH at time T₅, which is two slots afterthe end of the FPDCH transmission at time T₄.

[0060] At time T₆, a one-slot message is transmitted on the F-PDCCH foranother subpacket assignment. This message indicates the retransmissionof subpacket ‘1’ for the current encoder packet on the first ARQchannel, with SPID=‘1’ and ACID=‘0’. Since the duration of the F-PDCCHmessage is one slot, the duration of the subpacket transmission on theF-PDCH is also one slot. The terminal then combines the receivedsubpackets ‘0’ and ‘1’ and attempts to decode the encoder packet for thefirst ARQ channel. In this example, the terminal fails to correctlydecode the encoder packet based on the received subpackets ‘0’ and ‘1’.The terminal then sends a NAK on the R-ACKCH at time T₈, which is twoslots after the end of the F-PDCH transmission at time T₇.

[0061] In general, the receiver HARQ-CF may or may not provide ACKfeedback for each subpacket transmitted for the receiver. The followingscenarios cover each subpacket transmission:

[0062] If the receiver fails to receive the control information on theF-PDCCH, then it is unaware of the existence of the subpackettransmission. No feedback would then be transmitted by the receiver onthe R-ACKCH for this subpacket transmission.

[0063] If the receiver receives the control message correctly but failsto recover the HARQ packet based on all the subpackets received for theparticular encoder packet on the F-PDCH, then it is aware of thesubpacket transmission and sends a NAK back to the transmitter.

[0064] If the receiver receives the control message on the F-PDCCH andis also able to recover the HARQ packet based on the subpackets receivedon the F-PDCH, then it sends an ACK back to the transmitter.

[0065] For each transmitted subpacket, the transmitter performs theappropriate responsive action based on the feedback (or lack thereof)received from the receiver. In particular, the transmitter performs thefollowing:

[0066] If an ACK feedback is not received from the receiver for asubpacket transmission, then the transmitter HARQ-CF may retransmitanother subpacket for the HARQ packet on the same ARQ channel. Thetransmitter HARQ-CF may transmit up to a certain maximum number ofsubpackets (e.g., 8) for each HARQ packet.

[0067] If an ACK is received for a subpacket transmission, then thetransmitter HARQ-CF stops the transmission/retransmission of anyadditional subpacket for the encoder packet.

[0068] The RLP and HARQ-CF entities at the transmitter and receiver areused to provide reliable data transmission on the packet data channel.The functions performed by each of these entities are summarized below.In the following description, a ⁴“missing” packet is one that has notyet be recovered/received by a particular entity, but which may belongto an incomplete encoder packet transmission transaction and thus may berecovered/received subsequently. A “lost” packet is one that aparticular entity determines will not be recovered/received.

[0069] Transmitter HARO-CF: This entity determines whether or not agiven HARQ packet has been successfully delivered to the receiver byobserving the ACK/NAK feedback received on the R-ACKCH. The transmitterHARQ-CF does not comprehend the contents of the HARQ packet. Thereliance on the feedback on the R-ACKCH means that the transmitterHARQ-CF is susceptible to the following errors:

[0070] ACK becomes NAK: This error would trigger an unnecessarytransmission of an additional subpacket to the receiver.

[0071] NAK becomes ACK: This error is highly undesirable since the RLPwould then be relied upon to NAK each RLP frame included in the lostHARQ packet.

[0072] Transmitter RLP: This entity determines whether or not a givenRLP frame has been successfully delivered to the receiver by waiting fora NAK from the receiver RLP. With the addition of the HARQ-CF incdma2000 Release C, the transmitter RLP may need to wait for a long timebefore it receives the NAK from the receiver RLP for a missing RLPframe, as described below.

[0073] Receiver HARO-CF: This entity attempts to decode each encoderpacket sent by the transmitter HARQ-CF to recover the corresponding HARQpacket. If the receiver HARQ-CF receives a control message indicating asubpacket transmission for it, then it processes the F-PDCH to receivethe subpacket, accumulates all subpackets received thus far for theencoder packet being processed, and decodes the accumulated subpacket torecover the HARQ packet. Based on the result of the decoding, thereceiver HARQ-CF is able to determine whether or not the HARQ packet hasbeen recovered correctly without too much delay. The receiver HARQ-CFdoes not know what is contained inside the HARQ packet.

[0074] The receiver HARQ-CF is aware of the transmission and existenceof an encoder packet only if it detects at least one control message foreach of the following: (1) the previous subpacket, (2) the currentsubpacket, and (3) the next subpacket, which are transmitted with thesame ACID. In particular, the receiver HARQ-CF needs to observe thecolor bit flips in order to detect a new encoder packet. Consequently,the receiver HARQ-CF may not be able to immediately detect that anencoder packet has been transmitted (e.g., if it misses the controlmessage, in which case it would have to wait for the next subpackettransmission).

[0075] Receiver RLP: This entity can determine whether an RLP frame ismissing by looking at the sequence numbers of the received RLP frames.However, the receiver RLP is not able to determine within a short timeperiod whether the missing RLP frame is (1) part of an HARQ packet thatthe receiver HARQ-CF is still trying to recover via additional subpacketretransmission(s) or (2) part of a lost HARQ packet that will not berecovered by the receiver HARQ-CF. The receiver RLP would need to wait asufficient amount of time for the HARQ-CF retransmission to completebefore sending a NAK for an RLP retransmission. As a result, the delayfor the RLP retransmission of the missing RLP frame is typically long.

[0076] The HARQ-CF, which was added in cdma2000 Release C, extends thefunctionality of Layer 2 but impacts the operation of the RLP. Withoutthe HARQ-CF (in cdma2000 Release 0, A, and B), RLP frames can betransmitted in serial order to the receiver. The RLP is then used to (1)deliver RLP frames in-order to higher layers and (2) perform RLPretransmission. Therefore, if the receiver RLP detects that an RLP frameis missing, it can send back a NAK immediately and request the RLP frameto be retransmitted.

[0077] With the HARQ-CF (in cdma2000 Release C), multiple HARQ packetsmay be transmitted in parallel to the receiver, with each HARQ packetincluding one or more RLP frames. Moreover, the HARQ-CF cantransmit/retransmit each HARQ packet up to a specified maximum number oftimes until the HARQ packet is recovered correctly. As each HARQ packetis recovered by the receiver HARQ-CF, the RLP frame(s) included in therecovered HARQ packet are provided to the receiver RLP.

[0078] Since multiple HARQ packets may be transmitted in parallel by theHARQ-CF and since the RLP frame(s) in each HARQ packet may be sent bythe receiver HARQ-CF to the receiver RLP at different times depending onwhen the HARQ packet is recovered by the receiver HARQ-CF, it isdifficult for the receiver RLP to detect that a given RLP frame isactually lost. In particular, it is difficult for the receiver RLP todistinguish between two cases where (1) the lost RLP frame will not beprovided by the receiver HARQ-CF and needs to be retransmitted by theRLP and (2) the missing RLP frame is part of an HARQ packet that isstill being retransmitted by the HARQ-CF, which means that no RLPretransmission is required at this point.

[0079] In one RLP retransmission scheme to resolve the above ambiguity,the receiver RLP holds off requesting an RLP retransmission when itdetects a missing RLP frame. Instead, the receiver RLP waits for acertain amount of time to elapse before it sends a NAK for theretransmission request. The purpose for the delayed NAK is to give theHARQ-CF sufficient amount of time to finish up the transmission of theHARQ packet. This scheme is also referred to as a “delayed NAK” RLPretransmission scheme.

[0080]FIG. 5 is a diagram illustrating the interaction between thereceiver RLP and the receiver HARQ-CF for data transmission on thepacket data channel. This diagram also shows the operation of thedelayed NAK RLP retransmission scheme. In this example, three ARQchannels with ACIDs of ‘0’, ‘1’, and ‘2’ are used for the packet datachannel transmission. For simplicity, the subpacket transmissions forthis example are all of equal durations (i.e., same transmissionlengths) follow immediately one after another.

[0081] Starting at time T₁, the receiver HARQ-CF receives the controlmessage on the F-PDCCH indicating a subpacket transmission for it on ARQchannel ‘0’, processes the subpacket sent on this ARQ channel, andsuccessfully recovers the HARQ packet transmitted on ARQ channel ‘0’.The recovered HARQ packet is then passed to the multiplex sublayer,which then provides the RLP frames included in this HARQ packet to thereceiver RLP. The receiver HARQ-CF also transmits an ACK on the R-ACKCHat time T₃ for this HARQ packet.

[0082] For the next subpacket transmission starting at time T₂, thereceiver HARQ-CF fails to detect the control message on the F-PDCCH.Consequently, no HARQ packet is recovered by the receiver HARQ-CF, andno RLP frames are provided to the receiver RLP. Moreover, the receiverHARQ-CF does not transmit anything on the R-ACKCH for this subpackettransmission.

[0083] Starting at time T₄, the receiver HARQ-CF receives the controlmessage on the F-PDCCH indicating a subpacket transmission for it on ARQchannel ‘2’, processes the subpacket sent on this ARQ channel, andsuccessfully recovers the HARQ packet transmitted on ARQ channel ‘2’.This recovered HARQ packet is then passed to the multiplex sublayer,which then provides the RLP frames included in this HARQ packet to thereceiver RLP. The receiver HARQ-CF also transmits an ACK on the R-ACKCHat time T₆ for this HARQ packet.

[0084] Starting at time T₇, the receiver RLP receives the RLP framesincluded in the HARQ packet recovered from ARQ channel ‘2’. The receiverRLP looks at the sequence numbers of these RLP frames and those receivedearlier from ARQ channel ‘0’. The receiver RLP then determines thatthere are two missing RLP frames. However, instead of immediatelysending NAKs at the RLP sublayer to request retransmission of thesemissing RLP frames, the receiver RLP starts a delayed NAK timer forthese missing RLP frames. The receiver RLP would then send the NAKs atthe expiration of the delayed NAK timer.

[0085] Starting at time T₆, the receiver HARQ-CF receives the controlmessage on the F-PDCCH indicating a subpacket transmission for it on ARQchannel ‘0’, processes the subpacket sent on this ARQ channel, and failsto recover the HARQ packet transmitted on ARQ channel ‘0’. Theretransmission on ARQ channel ‘0’ is initiated by the transmitterHARQ-CF when it did not receive an ACK on the R-ACKCH for the HARQpacket sent earlier on this ARQ channel. Again, because the HARQ packetwas not recovered correctly, no RLP frames are provided to the receiverRLP. However, the receiver RLP transmits a NAK on the R-ACKCH at time T₉for this subpacket transmission.

[0086] The processing for subsequent subpacket transmissions occurs insimilar manner. As can be seen, the HARQ packets may be recovered in anunknown order by the receiver HARQ-CF. Consequently, the RLP framesprovided to receiver RLP may also be out of sequence with missing holes.

[0087] The delayed NAK RLP retransmission scheme described above worksif an appropriate value is selected for a delayed NAK timer. However,this timer value would need to be a very conservative value that wouldaccount for the longest possible retransmission delay for the HARQ-CFfor all ARQ channels in use. A large timer value would unduly affectsystem performance and efficiency since the receiver RLP would need towait for a long time before it can request the retransmission of eachmissing RLP frame.

[0088] Techniques are provided herein to exploit the functionality ofthe RLP and HARQ-CF so that they can operate in a seamless and efficientmanner to enhance system performance. These techniques utilize differentinformation available at different entities (e.g., the receiver RLP andreceiver HARQ-CF) to implement an RLP transmission scheme that providesimproved performance (e.g., at TCP) over the delayed NAK RLPretransmission scheme, which relies on delayed NAK with a conservativetimer value.

[0089] When the receiver RLP detects a missing RLP frame, the missingframe may still be in the process of being transmitted by the underlyingHARQ-CF. Therefore, the receiver RLP wants to wait for a certain amountof time to gain more confidence in its assessment that this RLP frame isreally lost. Ideally, the receiver RLP would send a NAK only after it istotally sure that the RLP frame is actually lost in order to avoidunnecessary retransmission of the RLP frame through a false-alarm NAK.However, the receiver RLP is blind of the operation of the underlyingHARQ-CF. Therefore, the value for the delayed NAK timer needs to beconservatively long.

[0090] In an aspect, a dynamic event-driven timer is maintained by thereceiver HARQ-CF for each RLP frame determined by the receiver RLP to bemissing. This dynamic timer has a variable duration and its expirationis triggered by events known to the receiver HARQ-CF, as described infurther detail below. The receiver RLP may also maintain a fixed timer(i.e., a delayed NAK timer with a fixed time duration) for each missingRLP frame. The receiver RLP may then send a NAK back to the transmitterRLP to request a retransmission of the missing RLP frame if either thedynamic timer or the fixed timer expires for the RLP frame, whicheveroccurs first.

[0091]FIG. 7 is a flow diagram of an embodiment of a process 700 forinitiating retransmission of missing RLP frames at the RLP sublayerbased on dynamic timers and fixed timers maintained for missing RLPframes.

[0092] Initially, the receiver RLP detects for missing RLP frames (step712). As shown in FIG. 5, this may be achieved by observing the sequencenumbers of RLP frames received by the receiver RLP, and identifyingmissing RLP frames as those that would fall between the RLP framesalready at the receiver RLP. If any missing RLP frames are detected,then the receiver RLP sends a “request” to the receiver HARQ-CF for thedetected missing RLP frames (step 714). The request asks the receiverHARQ-CF to maintain a dynamic timer for each missing RLP frame. In anembodiment, since RLP frames are identified by their sequence numbers,which are available to the receiver RLP but not to the receiver HARQ-CF,the receiver RLP provides the sequence numbers for the missing RLPframes along with each request it sends to the receiver HARQ-CF.

[0093] Upon receiving the request from the receiver RLP, the receiverHARQ-CF initiates a dynamic timer for each missing RLP frame that isidentified by the sequence number list included with the request (step722). Each dynamic timer maintained by the receiver HARQ-CF is thusassociated with the sequence number of a specific missing RLP frame. Thereceiver HARQ-CF thereafter maintains each dynamic timer and updates thedynamic timer state based on events known to the receiver HARQ-CF (step724). Each dynamic timer may also expire based on the occurrence ofcertain events, and different dynamic timers may be affected bydifferent events. The maintenance of the dynamic timers and theconditions for timer expiration are described in further detail below.

[0094] The receiver HARQ-CF sends an “indication” to the receiver RLPwhenever the dynamic timer for a given missing RLP frame expires (step726). If multiple dynamic timers expire for multiple missing RLP frames,then one indication may be sent for all such packets. In an embodiment,a list of sequence numbers of all missing RLP frames whose dynamictimers have expired is sent along with the indication. The indicationinforms the receiver RLP that the HARQ transmission/retransmissions forthese RLP frames are completely done and to not expect the receiverHARQ-CF to deliver these RLP frames. The receiver RLP would interpretthe indication to mean the identified missing RLP frames are indeedlost.

[0095] In the embodiment shown in FIG. 7, the receiver RLP alsoinitiates a fixed timer for each missing RLP frame (step 732). The valuefor the fixed timer may be configurable by the system at the start ofoperation on the packet data channel and may thereafter be fixed for theduration of the packet data channel operation. When the fixed timer fora missing RLP frame expires, the receiver RLP can send a “command” tothe receiver HARQ-CF to cancel the corresponding dynamic timermaintained by the receiver HARQ-CF for this RLP frame (step 734). Whenan once missing RLP frame is received after the dynamic timer for theframe is triggered, the receiver RLP can also send a command to thereceiver HARQ-CF to cancel the dynamic timer.

[0096] The receiver RLP receives the indication from the receiverHARQ-CF and “notification” of the expiration of any fixed timer (step742). The receiver RLP then initiates the recovery of each missing RLPframe whose fixed timer has expired or whose dynamic timer has expired(step 744). This RLP frame may be recovered via retransmission at theRLP sublayer. The steps shown in FIG. 7 may be performed periodically orat designated times. For example, the steps for the receiver RLP may beperformed whenever RLP frames are provided to the receiver RLP, and thesteps for the receiver HARQ-CF may be performed at the end of eachsubpacket transmission on the F-PDCH.

[0097] As noted above, the receiver HARQ-CF may be provided with a listof missing RLP frames by the receiver RLP. The receiver HARQ-CF is theninstructed to maintain a dynamic timer for each of the missing RLPframes. Each such dynamic timer expires when it is determined that themissing RLP frame will not be recovered by the receiver HARQ-CF.However, RLP frames are included in HARQ packets and since the receiverHARQ-CF does not know the contents of the recovered HARQ packets, it isnot able to specifically identify the RLP frames that were included inthe recovered HARQ packets.

[0098] Techniques are provided herein for the receiver HARQ-CF todetermine whether or not a particular missing RLP frame is lost withouthaving access to the sequence numbers of RLP frames that it may haverecovered. In an embodiment, this is achieved by successivelyeliminating all possible ARQ channels that may have been used totransmit the HARQ packet that includes the missing RLP frame, until noARQ channel is left. At this point, the missing RLP frame is deemed tobe lost and its dynamic timer expires.

[0099]FIG. 8 is a flow diagram of an embodiment of a process 800 fordetermining whether or not a particular missing RLP frame is lost basedon the subpacket transmissions on the F-PDCH. Process 800 may be usedfor each RLP frame detected to be missing by the receiver RLP. Process800 includes a set of steps 722a that initializes a dynamic timer forthe missing RLP frame and a set of steps 724a that updates the dynamictimer. Steps 722a may be used for step 722 in FIG. 7, and steps 724a maybe used for step 724.

[0100] Initially, a request is received from the receiver RLP tomaintain a dynamic timer for the missing RLP frame (step 812). Uponreceiving the request, the receiver HARQ-CF initializes a candidate setto include all possible ARQ channels that may be used to transmit theHARQ packet that includes the missing RLP frame (step 814). Thiscandidate set typically includes all ARQ channels assigned to thereceiver for packet data channel transmission, except for the ARQchannel that just delivered a set of good RLP frames to the receiver RLP(which is referred to as the “omitted” ARQ channel).

[0101] As shown in FIG. 5, the receiver RLP is able to detect that aparticular RLP frame is missing at near time T₇ after it has received aset of good RLP frames that were included in a good HARQ packetrecovered from a particular ARQ channel. This ARQ channel could not havebeen the one used to transmit the bad HARQ packet with the missing RLPframes, since the transmitter HARQ-CF would not have sent the good HARQpacket on the same ARQ channel until the bad HARQ packet had beensuccessfully recovered by the receiver HARQ-CF.

[0102] Referring back to FIG. 8, steps 812 and 814 are performed onceupon receiving the request, to initialize the dynamic timer for themissing RLP frame. Thereafter, the dynamic timer is updated byperforming steps 820 through 848. The updating may be achieved byevaluating each ARQ channel in the candidate set to determine whether ornot it could be the one used to transmit the HARQ packet that includesthe missing RLP frame.

[0103] When the dynamic timer is initialized, the terminal waits for thereception of the next subpacket dedicated to the terminal (step 820).When the next subpacket is received and the corresponding PDCH isprocessed, the dynamic timer updating commences by selecting the firstARQ channel in the candidate set for evaluation (step 822). Adetermination is then made whether or not an HARQ packet has beensuccessfully recovered from this ARQ channel (step 824). If the answeris yes, then this ARQ channel is removed from the candidate set (step830). The rational for removing this ARQ channel is the same as for notincluding the omitted ARQ channel in the candidate set. If the missingRLP frame is transmitted on the ARQ channel, then the receiver RLP willcancel this dynamic timer upon receiving the corresponding RLP frame.

[0104] Otherwise, after step 824, a determination is made whether or nota new HARQ packet has been transmitted on the ARQ channel (step 826). A“new” HARQ packet denotes a new HARQ packet that starts beingtransmitted after the dynamic timer is initialized. If the answer isyes, then this ARQ channel is removed from the candidate set (step 830).The new HARQ packet may have been transmitted on this ARQ channel forany one of several reasons. First, the transmitter HARQ-CF may transmita new HARQ packet after a maximum number of transmission/retransmissionof a prior HARQ packet, which may have included the missing RLP frame.Second, the transmitter HARQ-CF may have erroneously detected an ACK bitfor the prior HARQ packet and assumed that the prior HARQ packet wascorrectly recovered. In any case, the receiver HARQ-CF can be confidentthat no additional subpacket transmissions for the prior HARQ packetwill be sent on this ARQ channel. Thus, the ARQ channel may be removedfrom the candidate set.

[0105] The transmission of a new HARQ packet on the ARQ channel may bedetected by observing the color bit sent on the F-PDCCH for eachsubpacket transmission. As noted above, the color bit is toggled foreach new HARQ packet sent on the ARQ channel. Denote a “new” HARQ packetas a new HARQ packet that starts being transmitted after the dynamictimer is initialized, and the “previous” HARQ packet as the HARQ packetthat is already being transmitted when the dynamic timer is initialized.At the time when the dynamic timer is initialized, if the terminaldetects the presence of the “previous” HARQ packet, the transmission ofa “new” HARQ packet may be detected by observing the color bit for theARQ channel flips once (i.e., a change from the old value for the priorHARQ packet to the new value for the new HARQ packet). However, thereceiver HARQ-CF may fail to detect the presence of the “previous” HARQpacket at the time when the dynamic timer is initialized. This usuallyhappens if the terminal fails to detect the associated control messagesof all prior subpackets for the encoder packet. In this case, when theterminal observes the first color bit change after the dynamic timer isinitialized, it just detects the presence of the “previous” HARQ packet.In order to detect the presence of the “new” HARQ packet (and thecompletion of the “previous” HARQ packet), the terminal needs to observetwo color bit value changes. Thus, a “new” HARQ packet may be detectedwith greater confidence by observing the color bit flips twice.

[0106] Otherwise, after step 826, a determination is made whether or notany subpacket transmission has been received on this ARQ channel withinthe past period T_(m) (step 828). In one embodiment, this time periodcorresponds to M consecutive times that the receiver is scheduled afterthe dynamic timer is initialized. The parameter M may be selected basedon various factors such as, for example, (1) the total number of ARQchannels assigned to the receiver for packet data channel transmission,and (2) the maximum number of transmission/retransmissions for each HARQpacket. In general, M is set bigger if the likelihood of using the ARQchannel is less, which is the case if more ARQ channels are assigned orfewer retransmissions are permitted. In one specific embodiment, M maybe set as follows:

#ARQ channel≦M≦α·(#ARQ channel),

[0107] where α is a suitably selected constant greater than one. If theanswer for step 828 is yes, then this ARQ channel is removed from thecandidate set (step 830).

[0108] In one embodiment, the testing can be implemented by setting up acounter for each ARQ channel in the candidate set. Each counter isinitialized to zero. The counter for a particular ARQ channel incrementswhen a subpacket is received for the terminal but on some other ARQchannel. The counter is reset to zero when a subpacket is received forthe terminal and on this ARQ channel. When the counter reaches M, theARQ channel is removed from the candidate set.

[0109] A scheduler at the transmitter typically gives higher priority toencoder packets that have been in a transmit queue longer. Moreover,encoder packets are typically transmitted in an order based on theirpriorities. In this case, the pending HARQ packets are typicallyretransmitted according to their order in the transmit queue. Theparameter M may be selected based on and to account for the degree ofvalidity of the above two assumptions.

[0110] If the answer for step 828 is no or if the ARQ channel has beenremoved from the candidate set in step 830, then a determination is madewhether or not all ARQ channels in the candidate set have been evaluated(step 832). If the answer is no, then the next ARQ channel in the set isselected (step 834) and the process then returns to step 824 to evaluatethis ARQ channel.

[0111] Otherwise, if all ARQ channels in the set have been evaluated, asdetermined in step 832, then a determination is made whether or not thecandidate set is empty (step 842). If the candidate set is empty, thenthere is no ARQ channel that may be used to transmit the HARQ packetthat may include the missing RLP frame, and the dynamic timer for themissing RLP frame is set to expire (step 844). If the candidate set isnot empty but a command is received from the receiver RLP to cancel thedynamic timer (e.g., upon expiration of the fixed timer maintained bythe receiver RLP for the missing RLP frame or recovery of the missingframe), as determined in step 846, then the dynamic timer is canceled(step 848). Otherwise, if the candidate set is not empty and no commandsare received from the receiver RLP to cancel the dynamic timer, then theprocess returns to step 820 and the terminal waits for the nextsubpacket dedicated to it. The process terminates upon the expiration orcancellation of the dynamic timer.

[0112] The dynamic timer is updated periodically at the end of eachsubpacket reception on the F-PDCH. If the dynamic timer expires afterany update, then the receiver HARQ-CF can send an indication to thereceiver RLP for the missing RLP frame.

[0113] The process shown in FIG. 8 effectively determines a candidateset of all possible ARQ channels that may have been used to transmit theHARQ packet with the missing RLP frame and eliminates each ARQ channelin the candidate set that could not be used to transmit this HARQpacket. The missing RLP frame could still be retransmitted on any ARQchannels in the candidate set when the request is sent. By evaluatingdifferent events, the receiver HARQ-CF can eliminate the possibilitythat the RLP frame is still being transmitted on any one of the ARQchannels. This is the purpose for trimming down the candidate set. Oncethe receiver HARQ-CF determines that the missing RLP frame is no longerbeing transmitted on any of the ARQ channels, then it sends theindication. The process in FIG. 8 thus successively eliminates thepossible candidate ARQ channels.

[0114] Other criteria for eliminating possible ARQ channels from thecandidate set may also be used, and this is within the scope of theinvention. Moreover, it is not necessary to implement all three criteriashown in FIG. 8. For example, the criterion shown in step 828 may beomitted and the fixed timer maintained by the receiver RLP may be reliedupon to “time-out” the dynamic timer.

[0115] The ACK/NAK mechanism of the HARQ-CF below the RLP may beexploited to improve the reliability of data transmission on the packetdata channel. In one embodiment, when the transmitter HARQ-CF realizesthat a particular encoder packet is lost (after a certain number ofretransmissions for this encoder packet), the transmitter HARQ-CF canretransmit the encoder packet once more on the same ARQ channel but witha different color bit value. This will then force the receiver to purgeall subpackets that have been received for the encoder packet and startthe decoding process anew. This autonomous transmitter HARQ-CFretransmission scheme allows a lost encoder packet to be retransmittedwithout waiting for the delayed NAK from the receiver RLP, which mayoccur after a longer delay.

[0116] If autonomous retransmission by the transmitter HARQ-CF isemployed, then the updating of the dynamic timer for a missing RLP framein FIG. 8 may be modified to account for the possible retransmission ofthe same encoder packet with a new color bit value. In one embodiment,for step 826 in FIG. 8, a new HARQ packet may be detected to have beentransmitted on the ARQ channel if the color bit flips three times(instead of twice).

[0117] Other mechanisms for determining at the receiver HARQ-CF whetheror not a missing RLP frame is lost may also be implemented, and this iswithin the scope of the invention.

[0118]FIG. 6 is a diagram illustrating the interaction between thereceiver RLP and the receiver HARQ-CF for data transmission on thepacket data channel with the fixed and dynamic timers described above.The example of the packet data channel transmission in FIG. 6 is thesame as that described above for FIG. 5. In particular, three ARQchannels with ACIDs of ‘0’, ‘1’, and ‘2’ are used, and the subpackettransmissions are all of equal durations and follow immediately oneafter another.

[0119] As described above, near time T₇, the receiver RLP determinesthat there are two missing RLP frames with sequence numbers S2 and S3.The receiver RLP then starts a fixed timer for these missing RLP framesand also sends a request to the receiver HARQ-CF to start dynamic timersfor these frames.

[0120] Upon receiving the request, the receiver HARQ-CF starts twodynamic timers, Timer_A and Timer_B, for the two missing RLP frames withsequence numbers S2 and S3, respectively. To initialize these dynamictimers, the receiver HARQ-CF forms a candidate set for each missing RLPframe. The candidate sets C_(A) and C_(B) for Timer_A and Timer_B,respectively, would each include ACID=‘0’ and ACID=‘1’, but not ACID=‘2’since this ARQ channel provides the last good HARQ packet.

[0121] The receiver HARQ-CF then updates the active dynamic timers aftereach received subpacket transmission dedicated to the terminal. Shortlyafter time T₁₀, the receiver HARQ-CF determines that a good HARQ packetwas recovered from ARQ channel ‘0’, and ACID=‘0’ is removed from bothcandidate sets C_(A) and C_(B). Each candidate set would now onlyinclude ACID=‘1’. Shortly after time T₁₂, the receiver HARQ-CFdetermines that a good HARQ packet was recovered from ARQ channel ‘2’,which is not included in candidate sets C_(A) and C_(B). Thus, nochanges take place on candidate sets C_(A) and C_(B) for this subpackettransmission. Shortly after time T₁₄, the receiver HARQ-CF determinesthat a good HARQ packet was recovered from ARQ channel ‘1’, and ACID=‘1’is removed from both candidate sets C_(A) and C_(B). The receiverHARQ-CF then determines that candidate sets C_(A) and C_(B) are bothempty. As a result, the two dynamic timers, Timer_A and Timer_B, are setto expire. The receiver HARQ-CF would then send an indication to thereceiver RLP with sequence numbers S2 and S3 associated with the expiredTimer_A and Timer_B.

[0122] The example shown in FIG. 6 shows the removal of each ACID in thetwo candidate sets based on recovery of good HARQ packet on the ARQchannel. The other two criteria described in FIG. 8 for removing ARQchannels from the candidate sets were not invoked.

[0123] The techniques described herein may be used to provide improvedRLP retransmission for systems having an underlying HARQ retransmissionmechanism. These techniques may be used for various communicationsystems such as cdma2000 CDMA systems, W-CDMA systems, and so on. Thetechniques may also be applied to other communication systems having anupper retransmission mechanism (corresponding to the RLP) and a lowerretransmission mechanism (corresponding to the HARQ-CF). Thesetechniques may also be used for other types of communication systems(e.g., TDMA and FDMA systems).

[0124]FIG. 9 is a block diagram of an embodiment of base station 104 andterminal 106. On the forward link, data for the F-PDCH and F-PDCCH for aparticular terminal designated to receive packet data channeltransmission is received and processed (e.g., formatted, encoded, and soon) by a transmit (TX) data processor 912. The processing for the F-PDCHand F-PDCCH may be performed as described in the cdma2000 standarddocuments. The processed data is then provided to a modulator (MOD) 914and further processed (e.g., channelized, spread, and so on) to providemodulated data. A transmitter (TMTR) unit 916 then converts themodulated data into one or more analog signals, which are furtherconditioned (e.g., amplified, filtered, and frequency upconverted) toprovide a forward link signal. The forward link signal is routed througha duplexer (D) 922 and transmitted via an antenna 924 to the designatedterminal.

[0125] At the terminal, the forward link signal is received by anantenna 952, routed through a duplexer 954, and provided to a receiver(RCVR) unit 956. Receiver unit 956 conditions (e.g., filters, amplifies,and frequency downconverts) the received signal and further digitizesthe conditioned signal to provide samples. A demodulator 958 thenreceives and processes (e.g., despreads, channelizes, and datademodulates) the samples to provide symbols. Demodulator 958 mayimplement a rake receiver that can process multiple instances (ormultipath components) of the received signal to provide combinedsymbols. A receive (RX) data processor 960 then decodes the symbols,checks the received packets/frames, and provides the decoded data. Theprocessing by demodulator 958 and RX data processor 960 is complementaryto the processing by modulator 914 and TX data processor 912,respectively.

[0126] In one embodiment, RX data processor 960 performs the processingfor the physical layer and the HARQ-CF, and a controller 970 performsthe processing for the RLP. For this embodiment, RX data processor 960may provide (1) the decoded data for each HARQ packet recoveredcorrectly, (2) the status of each subpacket transmission (e.g., ACK orNAK), (3) indications of expired dynamic timers, and so on. Controller970 may then detect for missing RLP frames and provide request for RLPframes detected to be missing. Controller 970 further provides theappropriate NAK feedback for the receiver RLP to a TX data processor 982and the ACK/NAK feedback for the receiver HARQ-CF to a modulator 984.

[0127] On the reverse link, data for the reverse link and RLP feedbackinformation are processed (e.g., formatted, encoded, and so on) by TXdata processor 982, further processed (e.g., channelized, spread, and soon) by modulator 984, and conditioned (e.g., converted to analogsignals, amplified, filtered, and frequency upconverted) by atransmitter unit 986 to provide a reverse link signal. The reverse linksignal is then routed through duplexer 954 and transmitted via antenna952 to the base station.

[0128] At the base station, the reverse link signal is received byantenna 924, routed through duplexer 922, and provided to a receiverunit 942. Receiver unit 942 conditions (e.g., frequency downconverts,filters, and amplifies) the received signal and further digitizes theconditioned signal to provide a stream of samples. A demodulator 944then processes (e.g., despreads, channelizes, and so on) the samples toprovide symbols, and an RX data processor 946 further processes thesymbols to provide the decoded data for the terminal. The dataprocessing for the forward and reverse links is described by thecdma2000 standard documents.

[0129] A controller 930 receives the HARQ-CF ACKINAK feedback fromdemodulator 944 and the RLP NAK feedback from RX data processor 946 anddirects the appropriate retransmission for the HARQ-CF and RLP.

[0130] Controllers 930 and 970 further control the processing at thebase station and the terminal, respectively. Each controller may also bedesigned to implement all or a portion of the techniques describedherein for RLP retransmission. Program codes and data required bycontrollers 930 and 970 may be stored in memory units 932 and 972,respectively.

[0131] The techniques described herein for RLP retransmission may beimplemented by various means. For example, these techniques may beimplemented in hardware, software, or a combination thereof. For ahardware implementation, the elements used to implement the techniques(e.g., the elements that perform the processes shown in FIGS. 7 and 8)may be implemented within one or more application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof.

[0132] For a software implementation, these techniques may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory units 932 and 972 in FIG. 9) and executedby a processor (e.g., controllers 930 and 970). The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans as is known in the art.

[0133] The previous description of the disclosed embodiments is providedto enable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. In a wireless communication system with a firstretransmission mechanism in a first sublayer and a second retransmissionmechanism in a second sublayer, a method for retransmitting data withthe first retransmission mechanism, comprising: detecting for missingframes in the first sublayer; maintaining one or more dynamic timers forframes in the first sublayer detected to be missing; updating the one ormore dynamic timers based on events occurring in the second sublayer;and determining whether or not the frames detected to be missing arelost based on the one or more dynamic timers.
 2. The method of claim 1,wherein the first retransmission mechanism is provided by a Radio LinkProtocol (RLP).
 3. The method of claim 2, wherein the secondretransmission mechanism is provided by a hybrid automaticretransmission control function (HARQ-CF) that resides under the RLP. 4.The method of claim 1, wherein the events occurring in the secondsublayer correspond to transmission and retransmission of packets in thesecond sublayer.
 5. The method of claim 1, wherein one dynamic timer ismaintained for each frame in the first sublayer detected to be missing.6. The method of claim 5, wherein each missing frame may be transmittedon any one of a plurality of logical channels, and wherein the dynamictimer for each missing frame is associated with a respective candidateset of logical channels that may be used to transmit the missing frame.7. The method of claim 6, wherein the logical channels correspond to ARQchannels defined by cdma2000.
 8. The method of claim 6, wherein thedynamic timer for each missing frame expires if the associated candidateset is empty, and wherein the missing frame is deemed to be lost if thedynamic timer expires.
 9. The method of claim 6, wherein frames in thefirst layer are included in packets in the second layer, and wherein alogical channel is removed from a candidate set if a good packet in thesecond layer is received via the logical channel.
 10. The method ofclaim 9, wherein a logical channel is also removed from a candidate setif a new packet in the second layer is transmitted via the logicalchannel.
 11. The method of claim 9, wherein a logical channel is alsoremoved from a candidate set if no transmission is received via thelogical channel within a particular time period.
 12. The method of claim1, further comprising: maintaining one or more fixed timers for theframes detected to be missing, and wherein the one or more fixed timersare also used to determine whether or not the frames detected to bemissing are lost.
 13. The method of claim 1, further comprising: issuinga request to retransmit each frame in the first sublayer deemed to belost using the first retransmission mechanism.
 14. The method of claim1, further comprising: canceling each dynamic timer upon reception ofall frames associated wit h the dynamic timer.
 15. The method of claim1, wherein the wireless communication system is a cdma2000 system. 16.The method of claim 1, wherein the wireless communication system is aW-CDMA system.
 17. In a CDMA communication system with a firstretransmission mechanism provided by a Radio Link Protocol (RLP) and asecond retransmission mechanism provided by a hybrid automaticretransmission control function (HARQ-CF), a method for retransmittingdata via the RLP, comprising: detecting for missing RLP frames;maintaining a dynamic timer for each RLP frame detected to be missing;updating each dynamic timer based on events known to the HARQ-CF; anddetermining whether or not each RLP frame detected to be missing is lostbased on the dynamic timer maintained for the RLP frame.
 18. The methodof claim 17, wherein each missing RLP frame may be transmitted on anyone of a plurality of ARQ channels, and wherein the dynamic timer foreach missing RLP frame is associated with a respective candidate set ofARQ channels that may be used to transmit the missing RLP frame.
 19. Themethod of claim 18, wherein RLP frames are included in HARQ packetstransmitted by the HARQ-CF.
 20. The method of claim 19, wherein an ARQchannel is removed from a candidate set if a good HARQ packet isreceived via the ARQ channel.
 21. The method of claim 19, wherein an ARQchannel is removed from a candidate set if a new HARQ packet istransmitted via the ARQ channel.
 22. The method of claim 19, wherein anARQ channel is also removed from a candidate set if no transmission isreceived via the ARQ channel within a particular time period.
 23. Themethod of claim 22, wherein the particular time period is selected basedon likelihood of receiving a transmission on a given ARQ channel. 24.The method of claim 18, wherein the dynamic timer for each missing RLPframe expires if the associated candidate set is empty, and wherein themissing RLP frame is deemed to be lost if the dynamic timer expires. 25.The method of claim 18, wherein each dynamic timer is associated with asequence number for a corresponding missing RLP frame.
 26. The method ofclaim 17, further comprising: maintaining one or more fixed timers forthe missing RLP frames, and wherein the one or more fixed timers arealso used to determine whether or not the missing RLP frames are lost.27. The method of claim 17, further comprising: issuing a negativeacknowledgment (NAK) via the RLP for retransmission of each RLP framedeemed to be lost.
 28. The method of claim 17, further comprising:receiving a command to cancel a particular dynamic timer; and cancelingthe particular dynamic timer in accordance with the command.
 29. Themethod of claim 17, further comprising: upon receiving an RLP framedetected to be missing, canceling the dynamic timer maintained for theRLP frame.
 30. A memory communicatively coupled to a digital signalprocessing device (DSPD) capable of interpreting digital information to:detect for missing frames in a first sublayer; maintain one or moredynamic timers for frames in the first sublayer detected to be missing;update the one or more dynamic timers based on events occurring in asecond sublayer, wherein the first and second sublayers respectivelyprovide first and second retransmission mechanisms; and determinewhether or not the frames detected to be missing are lost based on theone or more dynamic timers.
 31. An apparatus in a wireless communicationsystem with a first retransmission mechanism in a first sublayer and asecond retransmission mechanism in a second sublayer, comprising: meansfor detecting for missing frames in the first sublayer; means formaintaining one or more dynamic timers for frames in the first sublayerdetected to be missing; means for updating the one or more dynamictimers based on events occurring in the second sublayer; and means fordetermining whether or not the frames detected to be missing are lostbased on the one or more dynamic timers.
 32. The apparatus of claim 31,wherein the first retransmission mechanism is provided by a Radio LinkProtocol (RLP).
 33. The apparatus of claim 32, wherein the secondretransmission mechanism is provided by a hybrid automaticretransmission control function (HARQ-CF) that resides under the RLP.34. A receiver in a wireless communication system with a firstretransmission mechanism in a first sublayer and a second retransmissionmechanism in a second sublayer, comprising: a RX data processoroperative to process a data transmission to provided decoded data; and acontroller operative to detect for missing frames in the first sublayerbased on the decoded data, maintain one or more dynamic timers forframes in the first sublayer detected to be missing, update the one ormore dynamic timers based on events occurring in the second sublayer,and determine whether or not the frames detected to be missing are lostbased on the one or more dynamic timers.
 35. The receiver of claim 34,wherein the controller is further operative to issue a request toretransmit each frame in the first sublayer deemed to be lost using thefirst retransmission mechanism.
 36. A terminal comprising the receiverof claim
 34. 37. A terminal in a wireless communication system with afirst retransmission mechanism in a first sublayer and a secondretransmission mechanism in a second sublayer, comprising: a RX dataprocessor operative to process a data transmission to provided decodeddata; and a controller operative to detect for missing frames in thefirst sublayer based on the decoded data, maintain one or more dynamictimers for frames in the first sublayer detected to be missing, updatethe one or more dynamic timers based on events occurring in the secondsublayer, and determine whether or not the frames detected to be missingare lost based on the one or more dynamic timers.
 38. The terminal ofclaim 37, wherein the wireless communication system is a cdma2000system.